The present invention generally relates to air conditioning and refrigeration systems and more particularly to a valving system for an air conditioning system for use in conjunction with interior confined space, which exhibits significantly improved energy efficiency at low outdoor ambient temperatures.
Air conditioning systems comprising a compressor, a condenser, expansion valve(s), and an evaporator associated in a cyclical relationship, have two basic temperature variables placed upon them to which they must respond. One variable is the load placed on the evaporator which piece of equipment is located within a confined space which is to be cooled. The second variable placed upon the air conditioning system is the outdoor ambient temperature to which the condenser is subject. While virtually all air conditioning and refrigeration systems must respond to the same outdoor ambient temperature placed upon the condenser, the evaporator loads may vary drastically depending upon the intended use of the system. For example, refrigeration systems may be utilized for maintaining frozen-food cases in grocery stores wherein extremely low temperature must be maintained, but a substantially constant load is placed upon the evaporator. Another example concerns air conditioning loads placed upon systems designed to maintain the temperature within large buildings. Dramatic temperature differentials between one side of the building facing the sun and the opposing side in the shade cause very great variable loads to be placed upon the evaporator.
Another class of air conditioning systems involves designs structured to maintain specific rooms or sections interiorly located of a building at a substantially constant temperature and humidity. Such systems are required, for example, to maintain proper computer room environments. These systems must be capable of recourse to variable loads placed upon the evaporator to maintain substantially constant temperature and humidity conditions within the enclosed space. While the such loads as are witnessed within computer room environments generally are normally substantially constant, the system must be effectively responsive should variable load conditions be placed upon it.
Regardless of the particular air conditioning or refrigeration system under consideration, its location in regions which are subject to distinct seasonal temperature variations can strain its performance especially during winter months when the condenser is subject to low outdoor ambient temperatures. As the outdoor ambient temperature decreases, a corresponding decrease in the head pressure from the compressor occurs. As the head pressure decreases, an adequate pressure drop across the expansion valving becomes difficult to maintain. A variety of techniques have been proposed to efficiently utilize the cold outdoor temperature in providing additional cooling capacity for air conditioning systems. The state of the art technique from which the present invention has application is described in commonly-assigned application of Sillato and Baer, U.S. Ser. No. 06/565,407, filed Dec. 17, 1983, the disclosure of which is expressly incorporated herein by reference. The Sillato et al. system maintains constant the set point of the temperature and/or humidity of a confined space or body, at variable heat loads therein, while the condenser is subjected to variable condenser temperature, eg. due to variable outdoor air temperature. Improved efficiencies for the system are achieved through the incorporation of variable speed, ie. capacity, compressor means responsive to varying condenser temperature, eg. varying outdoor air temperature, for attenuating liquid refrigerant mass flow during periods of lower outdoor air temperatures; and expansion means which maintain adequate mass flow of refrigerant to the evaporator for maintaining, for example, the desired set point of the temperature and/or humidity of the confined space, throughout the varying outdoor air temperatures. The energy efficiency ratio of the Sillato et al. system is improved as successively lower outdoor ambient air temperatures, ie. condenser temperatures, are witnessed.